In prior art, PMW switch power supply with backup battery is arranged, however, the general structure is to adopt multiple diodes for the isolation of two power supply units to prevent mutual flowing backward of two power supplies, two diodes are series connected to the output end of the battery to prevent charge of switch power supply to battery, and an isolation diode is series connected to the output end of the switch power supply to prevent the flowing backward of switch power supply from electric current of battery, and prevent the fast consumption of battery energy so as to lose backup function.
In light of higher requirements on conversion efficiency of power supply in every country and shortcomings existed in existing isolation technology, the isolation diode at the output end of the switch power supply will reduce output power of switch power supply greatly and increase conversion efficiency of switch power supply, which is badly in need of improvement.